@Kevin_Z it is clear that there is a BIG problem with this router. It is not a matter to update, change cables.... it is a BUG in the system. Unfortunately looks TPlink doesn't know how to solve it....

@Kevin_Z After 3 days I could confirm. There is a BUG. The connection was fine until yesterday, then it dropped again to 100Mb today. I checked the Negotiation Speed Setting and it was fine -> 1000...

@Kevin_Z Looks there is a BUG, because, after doing all the changes, the speed was ok, but suddely the limit was estabished again around 100Mb. Without any change in the configuration, I turned off...